Quarterly Data (Unaudited) - Quarterly Operating Results (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended													12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Selected Quarterly Financial Information [Line Items]
Operating Revenues	$ 7,255		$ 6,912		$ 6,024		$ 7,237		$ 6,163	$ 6,502	$ 6,141	$ 6,082		$ 27,429	[1]	$ 24,888	[1]	$ 23,489	[1]
Operating Income	348		1,739	[2]	842	[2]	168	[2]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	18	[3]	993		522		90		495	738	490	(4)	[4]	1,820		1,729		1,171
Reclassifications to Operating Income (Loss)			339		13		5
Unrecognized Tax Benefits, Interest on Income Taxes Accrued												265
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	4,802		4,412		3,789		4,390		3,772	4,255	4,070	3,533		17,393		15,630		14,437
Operating Income	(105)		1,225	[5]	441	[5]	(384)	[5]	405
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(91)		771		340		(185)		269	490	330	(18)		1,019		1,060		558
Reclassifications to Operating Income (Loss)			338		12		5			8		5
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	1,079		1,222		1,128		1,134		1,068	1,156	1,080	1,160		4,564		4,464		5,443
Operating Income	196		288	[6]	259	[6]	238		236	278	232	209
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	73		126		111		98		109	126	96	(81)		408		249		379
Reclassifications to Operating Income (Loss)			1		1
Unrecognized Tax Benefits, Interest on Income Taxes Accrued												170
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	750		693		656		993		805	728	672	895		3,094		3,100		3,186
Operating Income	156		133		134		149		168	155	138	203
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	98		81		84		89		102	92	72	121		352		395		381
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	761		697		653		1,054		794	737	653	880		3,165		3,065		2,735
Operating Income	113		102		55		169		101	114	69	163
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 52		$ 46		$ 16		$ 85		$ 47	$ 50	$ 22	$ 77		$ 211		$ 210		$ 4

[1] For the years ended December 31, 2014, 2013 and 2012, utility taxes of $89 million, $79 million and $82 million, respectively, are included in revenues and expenses for Generation. For the years ended December 31, 2014, 2013 and 2012, utility taxes of $238 million, $241 million and $239 million, respectively, are included in revenues and expenses for ComEd. For the years ended December 31, 2014, 2013 and 2012, utility taxes of $128 million, $129 million and $141 million, respectively, are included in revenues and expenses for PECO. For the years ended December 31, 2014, December 31, 2013 and for the period of March 12, 2012 through December 31, 2012, utility taxes of $86 million, $82 million and $59 million are included in revenues and expenses for BGE, respectively.

[2] In the first, second, and third quarter of 2014, Exelon reclassified $5 million, $13 million, and $339 million, respectively, to Operating income for presentation purposes in Exelon's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect Exelon's Net (Loss) Income on Common Stock.

[3] Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8—Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.

[4] Includes $265 million of interest expense related to the remeasurement of Exelon’s like-kind exchange tax position in the first quarter of 2013. See Note 14—Income Taxes of the Combined Notes to Consolidated Financial Statements for additional information.

[5] In the first, second, and third quarter of 2014, Generation reclassified $5 million, $12 million, and $338 million, respectively, to Operating (loss) income for presentation purposes in Generation's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect Generation's Net (Loss) Income on Membership Interest.

[6] In both the second and third quarter of 2014, ComEd reclassified $1 million to Operating income for presentation purposes in ComEd's Consolidated Statements of Operations and Comprehensive Income. The reclassifications did not affect ComEd's Net (Loss) Income.